Iron-based sintered alloy, iron base sintered alloy member, method for production thereof, and oil pump rotor

ABSTRACT

An iron-based sintered alloy member having a composition consisting of 0.5 to 7% by mass of Cu, 0.1 to 0.98% by mass of C, 0.02 to 0.3% by mass of oxygen and, optionally, 0.0025 to 1.05% by mass of Mn and/or 0.001 to 0.7% by mass of Zn, and the balance of Fe and inevitable impurities is manufactured by formulating an Fe powder, a graphite powder and a Cu alloy powder, as raw powders, mixing the powders to form a powder mixture, forming the powder mixture into a green compact and sintering the green compact. The Cu alloy powder has a composition consisting of 1 to 10% by mass of Fe, 0.2 to 1% by mass of oxygen and, optionally, 0.2 to 10% by mass of Zn and/or 0.5 to 15% by mass of Mn, and the balance of Cu and inevitable impurities.

TECHNICAL FIELD

The present invention relates to an iron-based sintered alloy and to aniron-based sintered alloy member, which are superior in dimensionalaccuracy, strength and slidability, to a method of manufacturing thesame, and to an oil pump rotor made of the iron-based sintered alloy.

BACKGROUND ART

With recent progress in methods of manufacturing iron-based sinteredalloy members, it has become possible to mass-produce various machineparts such as oil pump rotors with high accuracy using an iron-basedsintered alloy member which is superior in dimensional accuracy,strength, and slidability.

As an example of a method of manufacturing this kind of iron-basedsintered alloy member, there is provided a method of manufacturing aniron-based sintered alloy member which is superior in dimensionalaccuracy, strength and slidability, the method comprising press-forminga powder mixture, which is obtained by adding 0.01 to 0.20% of an oxidepowder such as aluminum oxide powder, titanium oxide powder, siliconoxide powder, vanadium oxide powder or chromium oxide powder to a powdermixture of an Fe powder, a Cu powder and a graphite powder, into a greencompact and sintering the green compact (see Japanese PatentApplication, First Publication No. Hei 6-41609).

Such an iron-based sintered alloy member has a texture composed of anaggregate of base material cells made of an Fe-based alloy containing Cuand C, which are partitioned with an old Fe powder boundary formed bysintering an Fe powder, and metal oxide grains are dispersed insidepores scattered in the texture, or dispersed along the old Fe powderboundary.

However, the iron-based sintered alloy member manufactured by the aboveconventional method is insufficient in dimensional accuracy andstrength, although the dimensional accuracy is improved to some degree,and therefore it has been required to develop a method of manufacturingan iron-based sintered alloy member which is markedly superior indimensional accuracy, strength and slidability. The resulting iron-basedsintered alloy member is not suited for use as a material of slidingmachine parts such as in an oil pump rotor.

DISCLOSURE OF THE INVENTION

A first aspect of the present invention is directed to a method ofmanufacturing an iron-based sintered alloy member having a compositionconsisting of, by mass (hereinafter percentages are by mass), 0.5 to 7%of Cu, 0.1 to 0.98% of C, 0.02 to 0.3% of oxygen, and the balance of Feand inevitable impurities, which comprises formulating an Fe powder, agraphite powder and a Cu alloy powder, as raw powders, mixing thepowders to form a powder mixture, forming the powder mixture into agreen compact and sintering the green compact, wherein the Cu alloypowder has a composition consisting of 1 to 10% of Fe, 0.2 to 1% ofoxygen, and the balance of Cu and inevitable impurities.

Further example of the first aspect of the present invention is directedto a method of manufacturing an iron-based sintered alloy member havinga composition consisting of 0.5 to 7% of Cu, 0.1 to 0.98% of C, 0.02 to0.3% of oxygen, 0.0025 to 1.05% of Mn, and the balance of Fe andinevitable impurities, which comprises formulating an Fe powder, agraphite powder and a Cu alloy powder, as raw powders, mixing thepowders to form a powder mixture, forming the powder mixture into agreen compact and sintering the green compact, wherein the Cu alloypowder has a composition consisting of at least one selected from thegroup consisting of 1 to 10% of Fe, 0.2 to 1% of oxygen and 0.5 to 15%of Mn, and the balance of Cu and inevitable impurities.

Yet another example of the first aspect of the present invention isdirected to a method of manufacturing an iron-based sintered alloymember having a composition consisting of 0.5 to 7% of Cu, 0.1 to 0.98%of C, 0.02 to 0.3% of oxygen, 0.001 to 0.7% of Zn, and the balance of Feand inevitable impurities, which comprises formulating an Fe powder, agraphite powder and a Cu alloy powder, as raw powders, mixing thepowders to form a powder mixture, forming the powder mixture into agreen compact and sintering the green compact, wherein the Cu alloypowder has a composition consisting of 1 to 10% of Fe, 0.2 to 1% ofoxygen, 0.2 to 10% of Zn, and the balance of Cu and inevitableimpurities.

Other examples of the first aspect of the present invention are directedto a method of manufacturing an iron-based sintered alloy member havinga composition consisting of 0.5 to 7% of Cu, 0.1 to 0.98% of C, 0.02 to0.3% of oxygen, 0.0025 to 1.05% of Mn, 0.001 to 0.7% of Zn, and thebalance of Fe and inevitable impurities, which comprises formulating anFe powder, a graphite powder and a Cu alloy powder, as raw powders,mixing the powders to form a powder mixture, forming the powder mixtureinto a green compact and sintering the green compact, wherein the Cualloy powder has a composition consisting of 1 to 10% of Fe, 0.2 to 1%of oxygen, 0.2 to 10% of Zn, 0.5 to 15% of Mn, and the balance of Cu andinevitable impurities.

Other examples of the first aspect of the present invention are directedto a method of manufacturing an iron-based sintered alloy member havinga composition consisting of 0.5 to 7% of Cu, 0.1 to 0.98% of C, 0.02 to0.3% of oxygen, 0.001 to 0.14% in total of at least one selected fromthe group consisting of Al and Si, and the balance of Fe and inevitableimpurities, which comprises formulating an Fe powder, a graphite powderand a Cu alloy powder, as raw powders, mixing the powders to form apowder mixture, forming the powder mixture into a green compact andsintering the green compact, wherein the Cu alloy powder has acomposition consisting of 1 to 10% of Fe, 0.2 to 1% of oxygen, 0.01 to2% in total of at least one selected from the group consisting of Al andSi, and the balance of Cu and inevitable impurities.

Other examples of the first aspect of the present invention are directedto a method of manufacturing an iron-based sintered alloy member havinga composition consisting of 0.5 to 7% of Cu, 0.1 to 0.98% of C, 0.02 to0.3% of oxygen, 0.0025 to 1.05% of Mn, 0.001 to 0.14% in total of atleast one selected from the group consisting of Al and Si, and thebalance of Fe and inevitable impurities, which comprises formulating anFe powder, a graphite powder and a Cu alloy powder, as raw powders,mixing the powders to form a powder mixture, forming the powder mixtureinto a green compact and sintering the green compact, wherein the Cualloy powder has a composition consisting of at least one selected fromthe group consisting of 1 to 10% of Fe, 0.2 to 1% of oxygen, 0.5 to 15%of Mn, 0.01 to 2% in total of at least one selected from the groupconsisting of Al and Si, and the balance of Cu and inevitableimpurities.

Other examples of the first aspect of the present invention are directedto a method of manufacturing an iron-based sintered alloy member havinga composition consisting of 0.5 to 7% of Cu, 0.1 to 0.98% of C, 0.02 to0.3% of oxygen, 0.001 to 0.7% of Zn, 0.001 to 0.14% in total of at leastone selected from the group consisting of Al and Si, and the balance ofFe and inevitable impurities, which comprises formulating an Fe powder,a graphite powder and a Cu alloy powder, as raw powders, mixing thepowders to form a powder mixture, forming the powder mixture into agreen compact and sintering the green compact, wherein the Cu alloypowder has a composition consisting of 1 to 10% of Fe, 0.2 to 1% ofoxygen, 0.2 to 10% of Zn, 0.01 to 2% in total of at least one selectedfrom the group consisting of Al and Si, and the balance of Cu andinevitable impurities.

Other examples of the first aspect of the present invention are directedto a method of manufacturing an iron-based sintered alloy member havinga composition consisting of 0.5 to 7% of Cu, 0.1 to 0.98% of C, 0.02 to0.3% of oxygen, 0.0025 to 1.05% of Mn, 0.001 to 0.7% of Zn, 0.001 to0.14% in total of at least one selected from the group consisting of Aland Si, and the balance of Fe and inevitable impurities, which comprisesformulating an Fe powder, a graphite powder and a Cu alloy powder, asraw powders, mixing the powders to form a powder mixture, forming thepowder mixture into a green compact and sintering the green compact,wherein the Cu alloy powder has a composition consisting of 1 to 10% ofFe, 0.2 to 1% of oxygen, 0.2 to 10% of Zn, 0.5 to 15% of Mn, 0.01 to 2%in total of at least one selected from the group consisting of Al andSi, and the balance of Cu and inevitable impurities.

A second aspect of the present invention is directed to an oil pumprotor made of an iron-based sintered alloy, comprising an iron-basedsintered alloy having a composition consisting of, by mass (hereinafterpercentages are by mass), 0.5 to 7% of Cu, 0.1 to 0.98% of C, 0.02 to0.3% of oxygen, and the balance of Fe and inevitable impurities.

Further examples of the second aspect of the present invention aredirected to an oil pump rotor made of an iron-based sintered alloy,comprising an iron-based sintered alloy having a composition consistingof 0.5 to 7% of Cu, 0.1 to 0.98% of C, 0.02 to 0.3% of oxygen, 0.0025 to1.05% of Mn, and the balance of Fe and inevitable impurities.

Yet further examples of the second aspect of the present invention aredirected to an oil pump rotor made of an iron-based sintered alloy,comprising an iron-based sintered alloy having a composition consistingof 0.5 to 7% of Cu, 0.1 to 0.98% of C, 0.02 to 0.3% of oxygen, 0.001 to0.7% of Zn, and the balance of Fe and inevitable impurities.

Other examples of the second aspect of the present invention aredirected to an oil pump rotor made of an iron-based sintered alloy,comprising an iron-based sintered alloy having a composition consistingof 0.5 to 7% of Cu, 0.1 to 0.98% of C, 0.02 to 0.3% of oxygen, 0.0025 to1.05% of Mn, 0.001 to 0.7% of Zn, and the balance of Fe and inevitableimpurities.

Other examples of the second aspect of the present invention aredirected to an oil pump rotor made of an iron-based sintered alloy,comprising an iron-based sintered alloy having a composition consistingof 0.5 to 7% of Cu, 0.1 to 0.98% of C, 0.02 to 0.3% of oxygen, 0.001 to0.14% in total of at least one selected from the group consisting of Aland Si, and the balance of Fe and inevitable impurities.

Other examples of the second aspect of the present invention aredirected to an oil pump rotor made of an iron-based sintered alloy,comprising an iron-based sintered alloy having a composition consistingof 0.5 to 7% of Cu, 0.1 to 0.98% of C, 0.02 to 0.3% of oxygen, 0.0025 to1.05% of Mn, 0.001 to 0.14% in total of at least one selected from thegroup consisting of Al and Si, and the balance of Fe and inevitableimpurities.

Other examples of the second aspect of the present invention aredirected to an oil pump rotor made of an iron-based sintered alloy,comprising an iron-based sintered alloy having a composition consistingof 0.5 to 7% of Cu, 0.1 to 0.98% of C, 0.02 to 0.3% of oxygen, 0.001 to0.7% of Zn, 0.001 to 0.14% in total of at least one selected from thegroup consisting of Al and Si, and the balance of Fe and inevitableimpurities.

Other examples of the second aspect of the present invention aredirected to an oil pump rotor made of an iron-based sintered alloy,comprising an iron-based sintered alloy having a composition consistingof 0.5 to 7% of Cu, 0.1 to 0.98% of C, 0.02 to 0.3% of oxygen, 0.0025 to1.05% of Mn, 0.001 to 0.7% of Zn, 0.001 to 0.14% in total of at leastone selected from the group consisting of Al and Si, and the balance ofFe and inevitable impurities.

A third aspect of the present invention is directed to an iron-basedsintered alloy which has a composition consisting of, by mass, 0.5 to10% of Cu, 0.1 to 0.98% of C, 0.02 to 0.3% of oxygen, and the balance ofFe and inevitable impurities, and also has a texture composed of anaggregate of base material cells made of an Fe-based alloy containing C,Cu and O, which are partitioned with an old Fe powder boundary formed bysintering an Fe powder, as raw powders, wherein the base material cellsmade of the Fe-based alloy containing C, Cu and O, which are partitionedwith the old Fe powder boundary, have such a gradient concentration thatthe concentration of Cu and O in the vicinity of the old Fe powderboundary is higher than the concentration of Cu and O of the centerportion of the base material cell.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic view showing concentration distribution of Cu andO of base material cells in the texture of an iron-based sintered alloyaccording to the present invention observed by EPMA.

BEST MODE FOR CARRYING OUT THE INVENTION First Aspect

The present inventors have intensively researched the manufacture of aniron-based sintered alloy member which is superior in dimensionalaccuracy, strength and slidability, and thus the following findings wereobtained.

(a) According to a conventional method of manufacturing an iron-basedsintered alloy member by formulating an Fe powder, a graphite powder anda Cu alloy powder, mixing the powders to form a powder mixture, formingthe powder mixture into a green compact and sintering the green compact,when the powder mixture of the Fe powder, the graphite powder and the Cupowder is sintered, the Cu powder is first melted during sintering toform a Cu liquid phase. Because of good wetting properties with Fe, theCu liquid phase penetrates into an Fe powder boundary, thereby causingbreakage of bonds between Fe powders. Therefore, the strength of theresulting sintered body decreases and the sintered body expands,resulting in poor dimensional accuracy.

(b) To improve the dimensional accuracy without decreasing the strengthof the sintered body, a Cu alloy powder containing 1 to 10% of Fe and0.2 to 1% of oxygen is used, as raw powders, in place of a Cu powder,and an Fe powder, graphite powder and the Cu alloy powder are mixed andformed into a green compact, which is then sintered. Consequently,wetting properties between the Cu liquid phase and the Fe powderdeteriorate and penetration of Cu into the Fe powder boundary issuppressed. Therefore, expansion of the sintered body is suppressed andthe dimensional accuracy is improved and, furthermore, bonding strengthbetween Fe powders does not decrease. When oxygen is not added in theform of a metal oxide, but in the form of a solid solution with a Cualloy powder, oxygen is concentrated in the portion having high Cuconcentration in the texture of the iron-based sintered alloy member,thereby improving the slidability. Therefore, an iron-based sinteredalloy member having a composition consisting of 0.5 to 7% of Cu, 0.1 to0.98% of C, 0.02 to 0.3% of oxygen, and the balance of Fe and inevitableimpurities obtained by this method is superior in dimensional accuracy,strength and slidability.

(c) When the Cu alloy powder used as raw powders is a Cu alloy powdercontaining 1 to 10% of Fe, 0.2 to 1% of oxygen and 0.5 to 15% of Mn, Mncan maintain the concentration of oxygen contained in the Cu alloypowder at a higher level and also increases the oxygen concentration ofa Cu liquid phase produced during sintering, thereby further suppressingpenetration of the Cu liquid phase into spaces between Fe grains.Consequently, expansion of the sintered body due to the Cu liquid phaseis suppressed, thereby further improving dimensional accuracy of thesintered body. Furthermore, the oxygen concentration of the portionhaving high Cu concentration in the texture of the iron-based sinteredalloy member increases, thereby improving slidability.

(d) When the Cu alloy powder used as raw powders is a Cu alloy powdercontaining 1 to 10% of Fe, 0.2 to 1% of oxygen and 0.2 to 10% of Zn, Zncan maintain the concentration of oxygen contained in the Cu alloypowder at higher level and also diffuses into Fe at a temperature lowerthan that of the Cu liquid phase, while Zn in Fe deteriorates wettingproperties between the Cu liquid phase and Fe grains. Therefore,expansion of the sintered body due to the Cu liquid phase is suppressed,thereby further improving dimensional accuracy of the sintered body.Thus, decrease in strength caused by breakage of Fe powders of the Culiquid phase is prevented and slidability is improved, thereby toimproving anti-seizing properties.

The method of manufacturing an iron-based sintered alloy memberaccording to a first aspect of the present invention has the followingconstitutions:

(A1) a method of manufacturing an iron-based sintered alloy memberhaving a composition consisting of 0.5 to 7% of Cu, 0.1 to 0.98% of C,0.02 to 0.3% of oxygen, and the balance of Fe and inevitable impurities,which comprises formulating an Fe powder, a graphite powder and a Cualloy powder, as raw powders, mixing the powders to form a powdermixture, forming the powder mixture into a green compact and sinteringthe green compact, wherein a powder having a composition consisting of 1to 10% of Fe, 0.2 to 1% of oxygen, and the balance of Cu and inevitableimpurities is used as the Cu alloy powder;

(A2) a method of manufacturing an iron-based sintered alloy memberhaving a composition consisting of 0.5 to 7% of Cu, 0.1 to 0.98% of C,0.02 to 0.3% of oxygen, 0.0025 to 1.05% of Mn, and the balance of Fe andinevitable impurities, which comprises formulating an Fe powder, agraphite powder and a Cu alloy powder, as raw powders, mixing thepowders to form a powder mixture, forming the powder mixture into agreen compact and sintering the green compact, wherein a powder having acomposition consisting of at least one selected from the groupconsisting of 1 to 10% of Fe, 0.2 to 1% of oxygen and 0.5 to 15% of Mn,and the balance of Cu and inevitable impurities is used as the Cu alloypowder;

(A3) a method of manufacturing an iron-based sintered alloy memberhaving a composition consisting of 0.5 to 7% of Cu, 0.1 to 0.98% of C,0.02 to 0.3% of oxygen, 0.001 to 0.7% of Zn, and the balance of Fe andinevitable impurities, which comprises formulating an Fe powder, agraphite powder and a Cu alloy powder, as raw powders, mixing thepowders to form a powder mixture, forming the powder mixture into agreen compact and sintering the green compact, wherein a powder having acomposition consisting of 1 to 10% of Fe, 0.2 to 1% of oxygen, 0.2 to10% of Zn, and the balance of Cu and inevitable impurities is used asthe Cu alloy powder; and

(A4) a method of manufacturing an iron-based sintered alloy memberhaving a composition consisting of 0.5 to 7% of Cu, 0.1 to 0.98% of C,0.02 to 0.3% of oxygen, 0.0025 to 1.05% of Mn, 0.001 to 0.7% of Zn, andthe balance of Fe and inevitable impurities, which comprises formulatingan Fe powder, a graphite powder and a Cu alloy powder, as raw powders,mixing the powders to form a powder mixture, forming the powder mixtureinto a green compact and sintering the green compact, wherein a powerhaving a composition consisting of 1 to 10% of Fe, 0.2 to 1% of oxygen,0.2 to 10% of Zn, 0.5 to 15% of Mn, and the balance of Cu and inevitableimpurities is used as the Cu alloy powder.

Since Al and Si components exert the effect of increasing the oxygenconcentration of the Cu alloy powder, a Cu alloy powder containing 0.01to 2% in total of at least one selected from the group consisting of Aland Si is used as raw powders and the Cu alloy powder is formulated,together with an Fe powder and a graphite powder, mixed and formed intoa green compact, which is then sintered. In this case, there can beobtained any one of the following four kinds of iron-based sinteredalloy members:

an iron-based sintered alloy member having a composition consisting of0.5 to 7% of Cu, 0.1 to 0.98% of C, 0.02 to 0.3% of oxygen, 0.001 to0.14% in total of at least one selected from the group consisting of Aland Si, and the balance of Fe and inevitable impurities;

an iron-based sintered alloy member having a composition consisting of0.5 to 7% of Cu, 0.1 to 0.98% of C, 0.02 to 0.3% of oxygen, 0.0025 to1.05% of Mn, 0.001 to 0.14% in total of at least one selected from thegroup consisting of Al and Si, and the balance of Fe and inevitableimpurities;

an iron-based sintered alloy member having a composition consisting of0.5 to 7% of Cu, 0.1 to 0.98% of C, 0.02 to 0.3% of oxygen, 0.001 to0.7% of Zn, 0.001 to 0.14% in total of at least one selected from thegroup consisting of Al and Si, and the balance of Fe and inevitableimpurities; and

an iron-based sintered alloy member having a composition consisting of0.5 to 7% of Cu, 0.1 to 0.98% of C, 0.02 to 0.3% of oxygen, 0.0025 to1.05% of Mn, 0.001 to 0.7% of Zn, 0.001 to 0.14% in total of at leastone selected from the group consisting of Al and Si, and the balance ofFe and inevitable impurities.

Therefore, the first aspect also includes the following methods:

(A5) a method of manufacturing an iron-based sintered alloy memberhaving a composition consisting of 0.5 to 7% of Cu, 0.1 to 0.98% of C,0.02 to 0.3% of oxygen, 0.001 to 0.14% in total of at least one selectedfrom the group consisting of Al and Si, and the balance of Fe andinevitable impurities, which comprises formulating an Fe powder, agraphite powder and a Cu alloy powder, as raw powders, mixing thepowders to form a powder mixture, forming the powder mixture into agreen compact and sintering the green compact, wherein the Cu alloypowder is a Cu alloy powder having a composition consisting of 1 to 10%of Fe, 0.2 to 1% of oxygen, 0.01 to 2% in total of at least one selectedfrom the group consisting of Al and Si, and the balance of Cu andinevitable impurities;

(A6) a method of manufacturing an iron-based sintered alloy memberhaving a composition consisting of 0.5 to 7% of Cu, 0.1 to 0.98% of C,0.02 to 0.3% of oxygen, 0.0025 to 1.05% of Mn, 0.001 to 0.14% in totalof at least one selected from the group consisting of Al and Si, and thebalance of Fe and inevitable impurities, which comprises formulating anFe powder, a graphite powder and a Cu alloy powder, as raw powders,mixing the powders to form a powder mixture, forming the powder mixtureinto a green compact and sintering the green compact, wherein the Cualloy powder is a Cu alloy powder having a composition consisting of atleast one selected from the group consisting of 1 to 10% of Fe, 0.2 to1% of oxygen and 0.5 to 15% of Mn, 0.01 to 2% in total of at least oneselected from the group consisting of Al and Si, and the balance of Cuand inevitable impurities;

(A7) a method of manufacturing an iron-based sintered alloy memberhaving a composition consisting of 0.5 to 7% of Cu, 0.1 to 0.98% of C,0.02 to 0.3% of oxygen, 0.001 to 0.7% of Zn, 0.001 to 0.14% in total ofat least one selected from the group consisting of Al and Si, and thebalance of Fe and inevitable impurities, which comprises formulating anFe powder, a graphite powder and a Cu alloy powder, as raw powders,mixing the powders to form a powder mixture, forming the powder mixtureinto a green compact and sintering the green compact, wherein the Cualloy powder is a Cu alloy powder having a composition consisting of 1to 10% of Fe, 0.2 to 1% of oxygen, 0.2 to 10% of Zn, 0.01 to 2% in totalof at least one selected from the group consisting of Al and Si, and thebalance of Cu and inevitable impurities; and

(A8) a method of manufacturing an iron-based sintered alloy memberhaving a composition consisting of 0.5 to 7% of Cu, 0.1 to 0.98% of C,0.02 to 0.3% of oxygen, 0.0025 to 1.05% of Mn, 0.001 to 0.7% of Zn,0.001 to 0.14% in total of at least one selected from the groupconsisting of Al and Si, and the balance of Fe and inevitableimpurities, which comprises formulating an Fe powder, a graphite powderand a Cu alloy powder, as raw powders, mixing the powders to form apowder mixture, forming the powder mixture into a green compact andsintering the green compact, wherein the Cu alloy powder is a Cu alloypowder having a composition consisting of 1 to 10% of Fe, 0.2 to 1% ofoxygen, 0.2 to 10% of Zn, 0.5 to 15% of Mn, 0.01 to 2% in total of atleast one selected from the group consisting of Al and Si, and thebalance of Cu and inevitable impurities.

The reasons for the compositions of the Cu alloy powder, as raw powdersused in the method of manufacturing the iron-based sintered alloy memberaccording to the first aspect, will now be described.

Fe contained in Cu alloy powder:

Fe is a component which deteriorates wetting properties with the Fepowder rather than the Cu powder and also suppresses expansion of thesintered body due to the Cu liquid phase by using it, as raw powders, inthe form of a Cu alloy powder containing 1 to 10% of Fe, and thusdimensional accuracy of the sintered body is further improved. When thecontent is less than 1%, desired effects cannot be obtained. On theother hand, when the content exceeds 10%, compressibility upon powdermolding deteriorates, and it is not preferable. Therefore, the amount ofFe contained in the Cu alloy powder was defined within a range from 1 to10%.

Oxygen contained in Cu alloy powder:

Oxygen contained in the Cu alloy powder concentrates oxygen in theportion having high Cu concentration and also improves dimensionalaccuracy, strength and slidability. When the content is less than 0.2%,it is made impossible to sufficiently concentrate oxygen in the portionhaving high Cu concentration. On the other hand, when the contentexceeds 1%, the strength of the iron-based sintered alloy memberobtained by sintering decreases, and it is not preferable. Therefore,the amount of oxygen contained in the Cu alloy powder was defined withina range from 0.2 to 1%.

Mn contained in Cu alloy powder:

Mn exerts the following effects. That is, Mn can maintain theconcentration of oxygen contained in the Cu alloy powder at a higherlevel and also increases the oxygen concentration in the Cu liquid phaseproduced during sintering, thereby suppressing penetration of the Culiquid phase into spaces between Fe grains, and thus expansion of thesintered body due to the Cu liquid phase is suppressed and dimensionalaccuracy of the sintered body is further improved. Also Mn increasesoxygen concentration of the portion having high Cu concentration in thetexture of the iron-based sintered alloy member, thereby improvingslidability. When the content is less than 0.5%, desired effects cannotbe obtained. On the other hand, when the content exceeds 15%, the amountof Mn contained in the iron-based sintered alloy member exceeds 1.05%,thereby deteriorating the toughness, and this is not preferable.Therefore, the amount of Mn contained in the Cu alloy powder was definedwithin a range from 0.5 to 15%.

Zn contained in Cu alloy powder:

Zn exerts the following effects. That is, Zn can maintain theconcentration of oxygen contained in the Cu alloy powder at a higherlevel and also diffuses into Fe at a temperature lower than that of theCu liquid phase. Zn in Fe deteriorates wetting properties between the Culiquid phase and Fe grains, and thus expansion of the sintered body dueto the Cu liquid phase is suppressed and dimensional accuracy of thesintered body is further improved. Also Zn prevents decrease in strengthdue to breakage of Fe powders of the Cu liquid phase and improves theslidability, thereby improving anti-seizing properties. When the contentis less than 0.2%, the amount of Zn contained in the iron-based sinteredalloy member becomes too small, such as 0.001 or less, and a desiredeffect cannot be obtained. On the other hand, when the content exceeds10%, the amount of Zn contained in the iron-based sintered alloy memberexceeds 0.7% and the toughness deteriorates, and it is not preferable.Therefore, the amount of Zn contained in the Cu alloy powder was definedwithin a range from 0.2 to 10%.

Al and Si contained in Cu alloy powder:

Al and Si are optionally added because they exert the effect ofincreasing the oxygen concentration of the Cu alloy powder. Even whenthe total amount of at least one selected from the group consisting ofAl and Si is less than 0.01%, the amount of Al and Si contained in theiron-based sintered alloy member is less than 0.001% and a desiredeffect cannot be obtained. On the other hand, when the total amount ofat least one selected from the group consisting of Al and Si exceeds 2%,the amount of Al and Si contained in the iron-based sintered alloymember exceeds 0.14% and the strength rather decreases, and it is notpreferable. Therefore, the amount of Al and Si contained in theiron-based sintered alloy member was defined within a range from 0.01 to2%.

Specifically, the method of manufacturing the iron-based sintered alloymember according to the first aspect may be a method comprisingpreparing a Cu alloy powder having a composition described in any of(A1) to (A8), as raw powders, preparing an Fe powder and a graphitepowder, formulating these raw powders in a predetermined amount, mixingthem with a zinc stearate powder or ethylenebisamide, as a lubricant, ina double corn mixer, press-forming the powder mixture into a greencompact, and sintering the green compact in a hydrogen atmospherecontaining nitrogen at a temperature of 1090 to 1300° C. The sinteringtemperature is more preferably from 1100 to 1260° C.

Second Aspect

The oil pump rotor according to the second aspect of the presentinvention employs the above iron-based sintered alloy member and has thefollowing constituents:

(B1) an oil pump rotor made of an iron-based sintered alloy, comprisingan iron-based sintered alloy having a composition consisting of 0.5 to7% of Cu, 0.1 to 0.98% of C, 0.02 to 0.3% of oxygen, and the balance ofFe and inevitable impurities;

(B2) an oil pump rotor made of an iron-based sintered alloy, comprisingan iron-based sintered alloy having a composition consisting of 0.5 to7% of Cu, 0.1 to 0.98% of C, 0.02 to 0.3% of oxygen, 0.0025 to 1.05% ofMn, and the balance of Fe and inevitable impurities;

(B3) an oil pump rotor made of an iron-based sintered alloy, comprisingan iron-based sintered alloy having a composition consisting of 0.5 to7% of Cu, 0.1 to 0.98% of C, 0.02 to 0.3% of oxygen, 0.001 to 0.7% ofZn, and the balance of Fe and inevitable impurities; and

(B4) an oil pump rotor made of an iron-based sintered alloy, comprisingan iron-based sintered alloy having a composition consisting of 0.5 to7% of Cu, 0.1 to 0.98% of C, 0.02 to 0.3% of oxygen, 0.0025 to 1.05% ofMn, 0.001 to 0.7% of Zn, and the balance of Fe and inevitableimpurities.

The oil pump rotor (B1) can be manufactured by formulating apredetermined amount of an Fe powder, a graphite powder and a Cu alloypowder having a composition consisting of 1 to 10% of Fe, 0.2 to 1% ofoxygen, and balance of Cu and inevitable impurities, as raw powders,mixing them with zinc stearate powder or ethylenebisamide, as alubricant, in a double corn mixer, press-forming the powder mixture intoa green compact, and sintering the green compact in a hydrogenatmosphere containing nitrogen at a temperature of 1090 to 1300° C.

The oil pump rotor (B2) can be manufactured by formulating apredetermined amount of an Fe powder, a graphite powder and a Cu alloypowder having a composition consisting of 1 to 10% of Fe, 0.2 to 1% ofoxygen, 0.5 to 15% of Mn, and balance of Cu and inevitable impurities,as raw powders, mixing them with zinc stearate powder orethylenebisamide, as a lubricant, in a double corn mixer, press-formingthe powder mixture into a green compact, and sintering the green compactin a hydrogen atmosphere containing nitrogen at a temperature of 1090 to1300° C.

The oil pump rotor (B3) can be manufactured by formulating apredetermined amount of an Fe powder, a graphite powder and a Cu alloypowder having a composition consisting of 1 to 10% of Fe, 0.2 to 1% ofoxygen, 0.2 to 10% of Zn, and balance of Cu and inevitable impurities,as raw powders, mixing them with zinc stearate powder orethylenebisamide, as a lubricant, in a double corn mixer, press-formingthe powder mixture into a green compact, and sintering the green compactin a hydrogen atmosphere containing nitrogen at a temperature of 1090 to1300° C.

The oil pump rotor (B4) can be manufactured by formulating apredetermined amount of an Fe powder, a graphite powder and a Cu alloypowder having a composition consisting of 1 to 10% of Fe, 0.2 to 1% ofoxygen, 0.2 to 10% of Zn, 0.5 to 15% of Mn, and balance of Cu andinevitable impurities, as raw powders, mixing them with zinc stearatepowder or ethylenebisamide, as a lubricant, in a double corn mixer,press-forming the powder mixture into a green compact, and sintering thegreen compact in a hydrogen atmosphere containing nitrogen at atemperature of 1090 to 1300° C.

Since the Al and Si components exert the effect of increasing the oxygenconcentration of the Cu alloy powder, an oil pump rotor made of aniron-based sintered alloy may be manufactured by using a Cu alloy powdercontaining 0.01 to 2% in total of at least one selected from the groupconsisting of Al and Si, as raw powders, formulating the Cu alloypowder, together with an Fe powder and a graphite powder, mixing them,forming the powder mixture, forming the powder mixture into a greencompact, and sintering the green compact.

In this case, there can be obtained the following oil pump rotors:

(B5) an oil pump rotor made of an iron-based sintered alloy, comprisingan iron-based sintered alloy having a composition consisting of 0.5 to7% of Cu, 0.1 to 0.98% of C, 0.02 to 0.3% of oxygen, 0.001 to 0.14% intotal of at least one selected from the group consisting of Al and Si,and the balance of Fe and inevitable impurities;

(B6) an oil pump rotor made of an iron-based sintered alloy, comprisingan iron-based sintered alloy having a composition consisting of 0.5 to7% of Cu, 0.1 to 0.98% of C, 0.02 to 0.3% of oxygen, 0.0025 to 1.05% ofMn, 0.001 to 0.14% in total of at least one selected from the groupconsisting of Al and Si, and the balance of Fe and inevitableimpurities;

(B7) an oil pump rotor made of an iron-based sintered alloy, comprisingan iron-based sintered alloy having a composition consisting of 0.5 to7% of Cu, 0.1 to 0.98% of C, 0.02 to 0.3% of oxygen, 0.001 to 0.7% ofZn, 0.001 to 0.14% in total of at least one selected from the groupconsisting of Al and Si, and the balance of Fe and inevitableimpurities; and

(B8) an oil pump rotor made of an iron-based sintered alloy, comprisingan iron-based sintered alloy having a composition consisting of 0.5 to7% of Cu, 0.1 to 0.98% of C, 0.02 to 0.3% of oxygen, 0.0025 to 1.05% ofMn, 0.001 to 0.7% of Zn, 0.001 to 0.14% in total of at least oneselected from the group consisting of Al and Si, and the balance of Feand inevitable impurities.

The oil pump rotor (B5) can be manufactured by formulating apredetermined amount of an Fe powder, a graphite powder and a Cu alloypowder having a composition consisting of 1 to 10% of Fe, 0.2 to 1% ofoxygen, 0.01 to 2% in total of at least one selected from the groupconsisting of Al and Si, and the balance of Cu and inevitableimpurities, as raw powders, mixing them with zinc stearate powder orethylenebisamide, as a lubricant, in a double corn mixer, press-formingthe powder mixture into a green compact, and sintering the green compactin a hydrogen atmosphere containing nitrogen at a temperature of 1090 to1300° C.

The oil pump rotor (B6) can be manufactured by formulating apredetermined amount of an Fe powder, a graphite powder and a Cu alloypowder having a composition consisting of 1 to 10% of Fe, 0.2 to 1% ofoxygen, 0.5 to 15% of Mn, 0.01 to 2% in total of at least one selectedfrom the group consisting of Al and Si, and the balance of Cu andinevitable impurities, as raw powders, mixing them with zinc stearatepowder or ethylenebisamide, as a lubricant, in a double corn mixer,press-forming the powder mixture into a green compact, and sintering thegreen compact in a hydrogen atmosphere containing nitrogen at atemperature of 1090 to 1300° C.

The oil pump rotor (B7) can be manufactured by formulating apredetermined amount of an Fe powder, a graphite powder and a Cu alloypowder having a composition consisting of 1 to 10% of Fe, 0.2 to 1% ofoxygen, 0.2 to 10% of Zn, 0.01 to 2% in total of at least one selectedfrom the group consisting of Al and Si, and the balance of Cu andinevitable impurities, as raw powders, mixing them with zinc stearatepowder or ethylenebisamide, as a lubricant, in a double corn mixer,press-forming the powder mixture into a green compact, and sintering thegreen compact in a hydrogen atmosphere containing nitrogen at atemperature of 1090 to 1300° C.

The oil pump rotor (B8) can be manufactured by formulating apredetermined amount of an Fe powder, a graphite powder and a Cu alloypowder having a composition consisting of 1 to 10% of Fe, 0.2 to 1% ofoxygen, 0.2 to 10% of Zn, 0.5 to 15% of Mn, 0.01 to 2% in total of atleast one selected from the group consisting of Al and Si, and thebalance of Cu and inevitable impurities, as raw powders, mixing themwith zinc stearate powder or ethylenebisamide, as a lubricant, in adouble corn mixer, press-forming the powder mixture into a greencompact, and sintering the green compact in a hydrogen atmospherecontaining nitrogen at a temperature of 1090 to 1300° C.

It was confirmed by EPMA (electron probe X-ray microanalysis) that theiron-based sintered alloy, which constitutes the oil pump rotor made ofthe iron-based sintered alloy having the composition of any one of (B1)to (B8) has such a texture that base material cells containing Fe, as amain component, Cu and O, which are partitioned with an old Fe powderboundary formed by sintering the Fe powder, as raw powders, areaggregated to form a basis material and the base material cellspartitioned with the old Fe powder boundary have such a gradientconcentration that the concentration of Cu and O in the vicinity of theold Fe powder boundary is higher than the concentration of Cu and O ofthe center portion of the base material cell. FIG. 1 is a schematic viewshowing concentration distribution of Cu and O in a base material cellof the oil pump rotor made of the iron-based sintered alloy of thepresent invention observed by EPMA. The area of dense dots correspondsto an area with high concentration of Cu and O. As shown in FIG. 1, basematerial cells containing Fe, as a main component, Cu and O, which arepartitioned with an old Fe powder boundary formed by sintering the Fepowder, as raw powders, are aggregated to form a basis material and thebase material cells have such a concentration that the concentration ofCu and O in the vicinity of the old Fe powder boundary is higher thanthe concentration of Cu and O of the center portion of the base materialcell. Therefore, the texture of the oil pump rotor made of theiron-based sintered alloy having the composition of any of (B1) to (B8)is different from a conventional texture wherein metal oxide grains aredispersed along the old Fe powder boundary.

The reason for the composition of the iron-based sintered alloyconstituting the oil pump rotor made of the iron-based sintered alloyaccording to the present invention will now be described.

Cu:

Cu is a component which improves sintering properties of the Fe powder,thereby improving dimensional accuracy of the resulting sintered body.When the amount of Cu contained in the iron-based sintered alloy is lessthan 0.5%, a desired effect cannot be obtained. On the other hand, whenthe amount exceeds 7%, the strength decreases, and it is not preferable.Therefore, the Cu content was defined within a range from 0.5 to 7%.

C:

C is a component which improves the strength and slidability of theiron-based sintered alloy. When the content is less than 0.1%, a desiredeffect cannot be obtained. On the other hand, when the content exceeds0.98%, the slidability and toughness of the iron-based sintered alloyobtained by sintering deteriorate, and it is not preferable. Therefore,the C content was defined within a range from 0.1 to 0.98%.

Oxygen:

In the iron-based sintered alloy wherein oxygen in the portion havinghigh Cu concentration in a basis material and in the vicinity of thebasis material is concentrated, the dimensional accuracy, strength andslidability are further improved. When the content is less than 0.02%,it is made impossible to sufficiently concentrate oxygen in the portionhaving high Cu concentration. On the other hand, when the contentexceeds 0.3%, the strength of the iron-based sintered alloy obtained bysintering decreases, and it is not preferable. Therefore, the amount ofoxygen contained in the iron-based sintered alloy was defined within arange from 0.02 to 0.3%. In this case, when oxygen is dispersed in theform of metal oxide grains, mating attackability increases, and thus itis necessary to incorporate oxygen in the form of a solid solution inthe portion having high Cu concentration.

Mn:

Mn exerts the following effects. That is, Mn can maintain theconcentration of oxygen contained in the Cu alloy powder at a higherlevel and also increases the oxygen concentration in the Cu liquid phaseproduced during sintering, thereby suppressing penetration of the Culiquid phase into spaces between Fe grains, and thus expansion of thesintered body due to the Cu liquid phase is suppressed and dimensionalaccuracy of the sintered body is further improved. Also Mn increasesoxygen concentration of the portion having high Cu concentration in thetexture of the iron-based sintered alloy member, thereby improvingslidability. When the content is less than 0.0025%, desired effectscannot be obtained. On the other hand, when the content exceeds 1.05%,the toughness of the iron-based sintered alloy deteriorates, and it isnot preferable. Therefore, the amount of Mn contained in the iron-basedsintered alloy was defined within a range from 0.0025 to 1.05%.

Zn:

Zn exerts the following effects. That is, Zn can maintain theconcentration of oxygen contained in the Cu alloy powder at a higherlevel and also diffuses into Fe at a temperature lower than that of theCu liquid phase. Zn in Fe deteriorates wetting properties between the Culiquid phase and Fe grains, and thus expansion of the sintered body dueto the Cu liquid phase is suppressed and dimensional accuracy of thesintered body is further improved. Also Zn prevents decrease in strengthdue to breakage of Fe powders of the Cu liquid phase and improves theslidability, thereby to improve anti-seizing properties. When thecontent is less than 0.001%, a desired effect cannot be obtained. On theother hand, when the amount contained in the iron-based sintered alloyexceeds 0.7%, the toughness deteriorates, and it is not preferable.Therefore, the amount of Zn contained in the iron-based sintered alloywas defined within a range from 0.001 to 0.7%.

Al and Si:

Al and Si are optionally added because they exert an effect ofincreasing the oxygen concentration of the Cu alloy powder. Even whenthe total amount of at least one selected from the group consisting ofAl and Si is less than 0.001%, a desired effect cannot be obtained. Onthe other hand, when the total amount of at least one selected from thegroup consisting of Al and Si exceeds 0.14%, the strength ratherdecreases, and it is not preferable. Therefore, the amount of Al and Sicontained in the iron-based sintered alloy was defined within a rangefrom 0.001 to 0.14%.

Third Aspect

The present inventors have intensively researched, and thus thefollowing findings were obtained.

(a) In a conventional iron-based sintered alloy obtained by formulatingan Fe powder, a graphite powder, a Cu alloy powder and a metal oxidepowder, mixing the powders to form a powder mixture, forming the powdermixture into a green compact and sintering the green compact, since thepowder mixture of the Fe powder, the graphite powder, the Cu alloypowder and the metal oxide powder is sintered, the Cu powder is firstmelted during sintering to form a Cu liquid phase. Because of goodwetting properties with Fe, the Cu liquid phase penetrates into an Fepowder boundary, thereby causing breakage of a bond between Fe powders.Therefore, the strength of the resulting sintered body decreases and thesintered body expands, resulting in poor dimensional accuracy. Also themetal oxide powder added is aggregated inside pores, or dispersed alongthe old Fe powder boundary, and thus a friction coefficient increases,thereby deteriorating sliding properties.

(b) To solve problems in conventional iron-based sintered alloys, a Cualloy powder containing 1 to 10% of Fe and 0.2 to 1% of oxygen is used,as raw powders, in place of a Cu powder, and an Fe powder, graphitepowder and the Cu alloy powder containing 1 to 10% of Fe and 0.2 to 1%of oxygen are mixed, and the resulting powder mixture is formed into agreen compact, which is then sintered. Consequently, penetration of Cualloy liquid phase into the Fe powder boundary is suppressed because ofpoor wetting properties between the Cu liquid phase produced duringsintering and the Fe powder. Therefore, expansion of the sintered bodyis suppressed and the dimensional accuracy is improved and, furthermore,bonding strength between Fe powders does not decrease. Since oxygen isadded in the form of a solid solution with a Cu alloy powder, oxygen isconcentrated in the portion having high Cu concentration in the textureof the iron-based sintered alloy member. Such a texture noticeablydecreases a friction coefficient as compared with a conventional texturewherein metal oxide grains are dispersed, thereby to improve slidingproperties. Therefore, an iron-based sintered alloy having a compositionconsisting of 0.5 to 10% of Cu, 0.1 to 0.98% of C, 0.02 to 0.3% ofoxygen, and the balance of Fe and inevitable impurities obtained by thismethod is superior in dimensional accuracy, strength and slidingproperties.

(c) An iron-based sintered alloy manufactured by using a Cu alloy powdercontaining 1 to 10% of Fe and 0.2 to 1% of oxygen, as raw powders, has atexture composed of an aggregate of base material cells made of anFe-based alloy containing C, Cu and O, which are partitioned with an oldFe powder boundary formed by sintering an Fe powder, as raw powders. Thebase material cells partitioned with the old Fe powder boundary havesuch a gradient concentration that the concentration of Cu and O islarge in the vicinity of the old Fe powder boundary and decreases towardthe center portion of the base material cell, though C is uniformlyincorporated into the base material cells in the form of a solidsolution.

The third aspect of the present invention has been made based on theresearch results described above and has the following constitution:

(C1) an iron-based sintered alloy which has a composition consisting of0.5 to 10% of Cu, 0.1 to 0.98% of C, 0.02 to 0.3% of oxygen, and thebalance of Fe and inevitable impurities, and also has a texture composedof an aggregate of base material cells made of an Fe-based alloycontaining C, Cu and O, which are partitioned with an old Fe powderboundary formed by sintering an Fe powder, as raw powders, wherein thebase material cells made of the Fe-based alloy containing C, Cu and O,which are partitioned with the old Fe powder boundary, have such agradient concentration that the concentration of Cu and O in thevicinity of the old Fe powder boundary is higher than the concentrationof Cu and O of the center portion of the base material cell.

The iron-based sintered alloy according to the third aspect of thepresent invention may contain at least one selected from the groupconsisting of N, Mo, Mn, Cr, Zn, Sn, P and Si for the purpose ofimproving the strength.

In the iron-based sintered alloy according to the third aspect of thepresent invention, the base material cells made of the Fe-based alloycontaining C, Cu and O, which are partitioned with the old Fe powderboundary, often have such a gradient concentration that theconcentration of Cu and O is maximum in the vicinity of the old Fepowder boundary, while the concentration of Cu and O decreases towardthe center portion of the base material cell and reached a minimum valueat the center of the base material cell, as a result of control of asintering time, and it is more preferable that the iron-based sinteredalloy have such a texture.

The iron-based sintered alloy according to the third aspect of thepresent invention further includes the following constitution:

(C2) an iron-based sintered alloy which has a composition consisting of,by mass, 0.5 to 10% of Cu, 0.1 to 0.98% of C, 0.02 to 0.3% of oxygen,and the balance of Fe and inevitable impurities, and also has a texturecomposed of an aggregate of base material cells made of an Fe-basedalloy containing C, Cu and O, which are partitioned with an old Fepowder boundary formed by sintering an Fe powder, as raw powders,wherein the base material cells made of the Fe-based alloy containing C,Cu and O, which are partitioned with the old Fe powder boundary, havesuch a gradient concentration that the concentration of Cu and O ismaximum in the vicinity of the old Fe powder boundary, while theconcentration of Cu and O decreases toward the center portion of thebase material cell and reached a minimum value at the center of the basematerial cell.

The iron-based sintered alloys having a composition consisting of 0.5 to10% of Cu, 0.1 to 0.98% of C, 0.02 to 0.3% of oxygen, and the balance ofFe and inevitable impurities described in (C1) and (C2) can bemanufactured by formulating a predetermined amount of an Fe powder, agraphite powder and a Cu alloy powder having a composition consisting of1 to 10% of Fe, 0.2 to 1% of oxygen, and the balance of Cu andinevitable impurities, as raw powders, mixing them with a zinc stearatepowder or ethylenebisamide, as a lubricant, in a double corn mixer,press-forming the powder mixture into a green compact, and sintering thegreen compact in a hydrogen atmosphere containing nitrogen at atemperature of 1090 to 1300° C.

The iron-based sintered alloy according to the third aspect of thepresent invention has a texture composed of an aggregate of basematerial cells made of an Fe-based alloy containing C, Cu and O, whichare partitioned with an old Fe powder boundary formed by sintering an Fepowder, as raw powders. The base material cells have such a gradientconcentration that the concentration of Cu and O in the vicinity of theold Fe powder boundary is higher than the concentration of Cu and O ofthe center portion of the base material cell. This was confirmed by EPMA(electron probe X-ray microanalysis).

FIG. 1 is a schematic view showing concentration distribution of Cu andO in base material cells, which are partitioned with an old Fe powderboundary of the texture of the iron-based sintered alloy of the presentinvention, observed by EPMA. The area of dense dots corresponds to anarea with high concentration of Cu and O. As shown in FIG. 1, basematerial cells containing Fe, as a main component, Cu and O, which arepartitioned with an old Fe powder boundary formed by sintering the Fepowder, as raw powders, are aggregated to form a basis material and thebase material cells partitioned with the old Fe powder boundary havesuch a concentration that the concentration of Cu and O in the vicinityof the old Fe powder boundary is higher than the concentration of Cu andO of the center portion of the base material cell. Therefore, thetexture of the iron-based sintered alloy having the composition of anyof (C1) to (C2) according to the third aspect of the present inventionis different from a conventional texture wherein metal oxide grains aredispersed along the old Fe powder boundary.

The reason for the composition of the iron-based sintered alloyaccording to the third aspect of the present invention will now bedescribed.

Cu:

Cu is a component which improves sintering properties of the Fe powder,thereby improving dimensional accuracy of the resulting sintered body.When the amount of Cu contained in the iron-based sintered alloy is lessthan 0.5%, a desired effect cannot be obtained. On the other hand, whenthe amount exceeds 10%, the strength decreases, and it is notpreferable. Therefore, the Cu content was defined within a range from0.5 to 10%.

C:

C is a component which improves the strength and sliding properties ofthe iron-based sintered alloy. When the content is less than 0.1%, adesired effect cannot be obtained. On the other hand, when the contentexceeds 0.98%, sliding properties and toughness of the iron-basedsintered alloy obtained by sintering deteriorate, and it is notpreferable. Therefore, the C content was defined within a range from 0.1to 0.98%.

Oxygen:

In the iron-based sintered alloy wherein oxygen in the portion havinghigh Cu concentration in a basis material and in the vicinity of thebasis material is concentrated, the dimensional accuracy, strength andslidability are further improved. When the content is less than 0.02%,it is made impossible to sufficiently concentrate oxygen in the portionhaving high Cu concentration. On the other hand, when the contentexceeds 0.3%, the strength of the iron-based sintered alloy obtained bysintering decreases, and it is not preferable. Therefore, the amount ofoxygen contained in the iron-based sintered alloy was defined within arange from 0.02 to 0.3%.

By using a Cu alloy powder containing 1 to 10% of Fe and 0.2 to 1% ofoxygen in place of the Cu powder, as raw powders, the resulting basematerial cells have such a gradient concentration that the concentrationof Cu and O in the vicinity of the old Fe powder boundary is higher thanthe concentration of Cu and O of the center portion of the base materialcell. The Cu alloy powder having a composition of 1 to 10% of Fe wasused as raw powders for the following reason. That is, when the contentof Fe is less than 1%, less effects of improving the dimensionalaccuracy of the sintered body is exerted, and it is not preferable. Onthe other hand, when the content of Fe exceeds 10%, the compressibilityupon formation into a green compact deteriorates, and it is notpreferable. The content of oxygen was controlled within a range from 0.2to 1% for the following reason. When the content of oxygen is less than0.2%, less effect of improving the dimensional accuracy of the sinteredbody is exerted, and it is not preferable. On the other hand, when thecontent of oxygen exceeds 1%, the toughness deteriorates, and it is notpreferable.

Example of First Aspect

As raw powders, an atomized Fe powder having an average grain size of 80μm, a graphite powder having an average grain size of 15 μm, Cu alloypowders A to U each having the average grain size and composition shownin Table 1, a pure Cu powder and a MnO powder were prepared. TABLE 1Composition (% by mass) Cu and inevitable Classification Fe O Mn Zn AlSi impurities Cu alloy A 1.2 0.25 — — — — balance powders B 4.1 0.36 — —— — balance C 9.5 0.52 — — — — balance D 5.2 0.35 0.8 — — — balance E3.8 0.68 6.5 — — — balance F 4.5 0.94 14.3 — — — balance G 2.9 0.31 —9.3 — — balance H 4.1 0.58 — 5.2 — — balance I 3.7 0.67 — 0.25 — —balance J 3.3 0.42 1.8 1.5 — — balance K 3.8 0.81 1.8 7.4 — — balance L5.2 0.88 0.58 0.84 — — balance M 4.4 0.45 — — — 0.03 balance N 4.7 0.42— — 0.03 — balance 0 4.1 0.77 — — 0.93 0.94 balance P 4.2 0.49 1.1 3.60.06 0.07 balance Q 3.7 0.50 7.6 2.2 0.04 0.06 balance R  0.5* 0.21 — —— — balance S 11*  0.45 — — — — balance T 3.8 0.1* — — — — balance U 6.71.2* — — — — balanceNote:symbol * denotes a value that is not within the scope of the firstaspect

These raw powders were formulated according to the compositions shown inTable 2 to Table 3 and mixed with zinc stearate powder, as a lubricantused upon metallic molding, in an amount of 0.8% in terms of an outerpercentage, and then the powder mixture was press-formed into abar-shaped green compact measuring 10 mm×10 mm×50 mm under a compactingpressure of 600 MPa. The resulting bar-shaped green compact was sinteredin an endothermic gas atmosphere under the conditions of a temperatureof 1140° C. for 20 minutes to obtain a bar-shaped test piece, andExamples A1 to A17, Comparative Examples A1 to A4 and ConventionalExample A1 were carried out.

The size of the bar-shaped test pieces made in Examples A1 to A17,Comparative Examples A1 to A4 and Conventional Example A1 was measuredand a dimensional change ratio of a standard size of the green compactwas determined. The dimensional accuracy was evaluated by the resultsshown in Table 2 to Table 3. A Charpy impact value was determined by aCharpy impact test. The results are shown in Table 2 to Table 3.Furthermore, the bar-shaped test pieces were machined to obtain tensiletest pieces. Using these tensile test pieces, tensile strength wasmeasured. The results are shown in Table 2 to Table 3.

Furthermore, wear test pieces each measuring 5 mm×3 mm×40 mm and a SS330(rolled steel for general structure) ring having an outer diameter of 45mm and an inner diameter of 27 mm were prepared by machining thebar-shaped test piece. Each wear test piece was pressed against the ringrotating at a rotation number of 1500 rpm and a rotational speed of 3.5m/second while increasing a pressing load, and then a load at whichseizing occurred was measured. The results are shown in Table 2 to Table3. TABLE 2 Composition of raw powder (% by mass) Cu alloy powder inGraphite Fe Composition of iron-based sintered alloy member (% by mass)Classification Table 1 powder powder Cu C O Mn Zn Al Si Fe Examples A1A: 6.7 1.15 balance 6.61 0.97 0.07 — — — — balance A2 B: 3 0.8 balance2.86 0.93 0.05 — — — — balance A3 C: 5 1.1 balance 4.50 0.92 0.11 — — —— balance A4 D: 5 1.1 balance 4.67 0.94 0.07 0.037 — — — balance A5 E: 41.0 balance 3.54 0.89 0.13 0.26 — — — balance A6 F: 7 1.0 balance 5.610.87 0.28 1.00 — — — balance A7 G: 6 1.0 balance 5.23 0.85 0.06 — 0.551— — balance A8 H: 2.5 0.8 balance 2.24 0.72 0.04 — 0.130 — — balance A9I: 1.5 0.7 balance 1.41 0.60 0.02 — 0.004 — — balance A10 J: 2 0.7balance 1.83 0.61 0.03 0.036 0.028 — — balance A11 K: 3 0.9 balance 2.560.78 0.09 0.051 0.220 — — balance A12 L: 1 0.2 balance 0.93 0.18 0.030.006 0.006 — — balance Dimensional Charpy impact Tensile Load uponClassification change ratio (%) value (J/cm²) strength (MPa) seizing (N)Examples A1 0.15 25 596 686 A2 0.05 18 620 588 A3 0.14 22 567 686 A40.13 24 537 686 A5 0.12 20 603 686 A6 0.15 25 575 980 A7 0.13 21 623 784A8 0.04 17 642 588 A9 0.03 19 562 490 A10 0.05 22 580 588 A11 0.04 21655 686 A12 0.13 17 573 490

TABLE 3 Composition of raw powder (% by mass) Cu alloy powder inGraphite Fe Composition of iron-based sintered alloy member (% by mass)Classification Table 1 powder powder Cu C O Mn Zn Al Si Fe Examples A13M: 3.5 0.9 balance 2.83 0.79 0.07 — — — 0.0011 balance A14 N: 3.5 0.8balance 2.84 0.70 0.05 — — 0.0012 — balance A15 O: 6.5 1.1 balance 6.030.9 0.21 — — 0.060 0.060 balance A16 P: 3 0.8 balance 2.68 0.71 0.050.632 0.103 0.0015 0.0021 balance A17 Q: 3 0.9 balance 2.58 0.78 0.060.227 0.050 0.0011 0.0015 balance Comparative A1 R: 3 0.9 balance 2.940.77 0.02 — — — — balance Examples A2 S: 3 0.9 balance 2.98 0.80 0.05 —— — — balance A3 T: 3 0.9 balance 2.65 0.78 0.01 — — — — balance A4 U: 30.9 balance 2.83 0.77 0.13 — — — — balance Conventional Pure Cu: 3 0.9balance 2.98 0.80 0.03 — — — — balance Example A1 MnO: 0.1 DimensionalCharpy impact Tensile Load upon Classification change ratio (%) value(J/cm²) strength (MPa) seizing (N) Examples A13 0.06 18 623 588 A14 0.0718 610 588 A15 0.14 25 629 980 A16 0.06 21 628 784 A17 0.02 19 644 882Comparative A1 0.23 12 394 196 Examples A2 0.15 9 421 294 A3 0.28 13 410196 A4 0.13 8 346 686 Conventional 0.36 7 375 196 Example A1

As is apparent from the results shown in Table 2 and Table 3, comparingExamples A1 to A17 with Conventional Example Al, test pieces made inExamples A1 to A17 are superior in dimensional accuracy because adimensional change ratio is smaller than that of the test piece made inConventional Example A1, and exhibits high Charpy impact value and hightensile strength, and is also superior in slidability because of lesswear amount of the ring. However, test pieces of Comparative Examples A1to A4, which use a Cu powder having a composition that is not within thescope of the first aspect, are inferior in at least one of dimensionalaccuracy, Charpy impact value, tensile strength and wear amount.

Example of Second Aspect

As raw powders, an atomized Fe powder having an average grain size of 80μm, a graphite powder having an average grain size of 15 μm, Cu alloypowders A to R each having the average grain size and composition shownin Table 4, a pure Cu powder, and a MnO powder were prepared. TABLE 4Composition (% by mass) Cu and inevitable Classification Fe O Mn Zn AlSi impurities Cu alloy A 1.2 0.25 — — — — balance powders B 4.1 0.36 — —— — balance C 9.5 0.52 — — — — balance D 5.2 0.35 0.8 — — — balance E3.8 0.68 6.5 — — — balance F 4.5 0.94 14.3 — — — balance G 2.9 0.31 —9.3 — — balance H 4.1 0.58 — 5.2 — — balance I 3.7 0.67 — 0.25 — —balance J 3.3 0.42 1.8 1.5 — — balance K 3.8 0.81 1.8 7.4 — — balance L5.2 0.88 0.58 0.84 — — balance M 4.4 0.45 — — — 0.03 balance N 4.7 0.42— — 0.03 — balance O 4.1 0.77 — — 0.93 0.94 balance P 4.2 0.49 1.1 3.60.06 0.07 balance Q 3.8 0.98 — — — — balance R 4.2 0.13 — — — — balance

These raw powders were formulated according to the compositions shown inTable 5 to Table 6 and mixed with zinc stearate powder, as a lubricantused upon metallic molding, in an amount of 0.8% in terms of an outerpercentage, and then the powder mixture was press-formed into abar-shaped green compact measuring 10 mm×10 mm×50 mm under a compactingpressure of 600 MPa. The resulting bar-shaped green compact was sinteredin an endothermic gas atmosphere under the conditions of a temperatureof 1140° C. for 20 minutes to obtain bar-shaped test pieces (hereinafterreferred to as Examples) B1 to B16 made of iron-based sintered alloys,which constitute the oil pump rotor of the present invention, eachhaving the composition shown in Table 5 to Table 6, bar-shaped testpieces (hereinafter referred to as Comparative Examples) B1 to B6 madeof iron-based sintered alloys which constitute the comparative oil pumprotor, and a bar-shaped test piece (hereinafter referred to asConventional Example) B1 made of an iron-based sintered alloy whichconstitutes the conventional oil pump rotor.

With regard to Examples B1 to B16, Comparative Examples B1 to B6 andConventional Example B1, concentration distribution of Cu and O in thebasis material was observed by EPMA. The results are shown in Table 5and Table 6.

The sizes of Examples B1 to B16, Comparative Examples B1 to B6 andConventional Example B1 were measured and a dimensional change ratio ofa standard size of the green compact was determined. The dimensionalaccuracy was evaluated by the results shown in Table 7.

A Charpy impact value was determined by a Charpy impact test. Theresults are shown in Table 7. Furthermore, Examples B1 to B16,Comparative Examples B1 to B6 and Conventional Example B1 were machinedto obtain tensile test pieces. Using these tensile test pieces, atensile strength was measured. The results are shown in Table 7.

Furthermore, wear test pieces each measuring 5 mm×3 mm×40 mm obtained bymachining Examples B1 to B16, Comparative Examples B1 to B6 andConventional Example B1 and a SS330 (rolled steel for general structure)ring having an outer diameter of 45 mm and an inner diameter of 27 mmwere prepared by machining the bar-shaped test piece. Each wear testpiece was pressed against the ring rotating at a rotation number of 1500rpm and a rotational speed of 3.5 m/second while increasing a pressingload, and then a load at which seizing occurred was measured. Theresults are shown in Table 7. TABLE 5 Composition of raw powder (% bymass) Cu alloy powder in Graphite Fe Composition (% by mass) Test piecesTable 4 powder powder Cu C O Mn Zn Al Si Fe Texture Examples B1 A: 6.71.15 balance 6.61 0.97 0.07 — — — — Fe The concentration of B2 B: 3 0.8balance 2.86 0.93 0.05 — — — — balance Cu and O in the vicinity B3 C: 51.1 balance 4.50 0.92 0.11 — — — — balance of an old Fe powder B4 D: 51.1 balance 4.67 0.94 0.07 0.037 — — — balance boundary is higher thanB5 E: 4 1.0 balance 3.54 0.89 0.13 0.26 — — — balance the concentrationof Cu B6 F: 7 1.0 balance 5.61 0.87 0.28 1.00 — — — balance and O of thecenter portion. B7 G: 6 1.0 balance 5.23 0.85 0.06 — 0.551 — — balanceB8 H: 2.5 0.8 balance 2.24 0.72 0.04 — 0.130 — — balance B9 I: 1.5 0.7balance 1.41 0.60 0.02 — 0.004 — — balance B10 J: 2 0.7 balance 1.830.61 0.03 0.036 0.028 — — balance B11 K: 3 0.9 balance 2.56 0.78 0.090.051 0.220 — — balance B12 L: 1 0.2 balance 0.93 0.18 0.03 0.006 0.006— — balance

TABLE 6 Composition of raw powder (% by mass) Cu alloy powder inGraphite Fe Composition (% by mass) Test pieces Table 4 powder powder CuC O Mn Zn Al Si Fe Texture Examples B13 M: 3.5 0.9 balance 2.83 0.790.07 — — — 0.0011 balance The concentra- B14 N: 3.5 0.8 balance 2.840.70 0.05 — — 0.0012 — balance tion of Cu and B15 O: 6.5 1.1 balance6.03 0.90 0.21 — — 0.060 0.060 balance O in the vicinity B16 P: 3 0.8balance 2.68 0.71 0.05 0.632 0.103 0.0015 0.0021 balance of an old FeCompar- B1 B: 7.5 0.9 balance  7.25* 0.77 0.02 — — — — balance powderboundary ative B2 B: 0.4 0.9 balance  0.33* 0.80 0.05 — — — — balance ishigher than Examples B3 B: 3 1.2 balance 2.65  1.01* 0.02 — — — —balance the concentra- B4 B: 3 0.1 balance 2.83  0.06* 0.13 — — — —balance tion of Cu and B5 Q: 3 0.9 balance 2.85 0.82 0.4* — — — —balance O of the center B6 R: 3 0.9 balance 2.85 0.81  0.01* — — — —balance portion. Conven- B1 Pure Cu: 3 0.9 balance 2.98 0.03 0.03 0.027— — — balance MnO grains are tional MnO: 0.1 dispersed in a Examplebasis material.Note:symbol * denotes a value that is not within the second aspect of thepresent invention

TABLE 7 Dimensional Charpy Load change impact Tensile upon ratio valuestrength seizing Test pieces (%) (J/cm²) (MPa) (N) Examples B1 0.15 25596 686 B2 0.05 18 620 588 B3 0.14 22 567 686 B4 0.13 24 537 686 B5 0.1220 603 686 B6 0.15 25 575 980 B7 0.13 21 623 784 B8 0.04 17 642 588 B90.03 19 562 490 B10 0.05 22 580 588 B11 0.04 21 655 686 B12 0.13 17 573490 B13 0.06 18 623 588 B14 0.07 18 610 588 B15 0.14 25 629 980 B16 0.0621 628 784 Comparative B1 0.42 10 431 294 Examples B2 0.10 7 238 196 B30.28 5 351 294 B4 0.38 10 225 196 B5  0.19* 8 251 294 B6 0.22 12 450 196Conventional 0.36 7 375 196 Example B1

As is apparent from the results shown in Table 5 to Table 7, comparingExamples B1 to B16 with Conventional Example B1, Examples B1 to B16 aresuperior in dimensional accuracy because a dimensional change ratio issmaller than that of Conventional Example B1, and exhibit high Charpyimpact value and high tensile strength, and also superior in slidabilitybecause of less wear amount of the ring.

However, Comparative Examples B1 to B6 having the composition that isnot within the scope of the second aspect are inferior in at least oneof dimensional accuracy, Charpy impact value, tensile strength and wearamount. Therefore, oil pump rotors made of an iron-based sintered alloyhaving the same composition as that of Examples B1 to B16 are superiorin dimensional accuracy, strength and slidability to an oil pump rotormade of a conventional iron-based sintered alloy.

Example of Third Aspect

As raw powders, an atomized Fe powder having an average grain size of 80μm, a graphite powder having an average grain size of 15 μm, Cu alloypowders A to L each having the average grain size and composition shownin Table 8, a pure Cu powder and a MnO powder were prepared. TABLE 8Composition (% by mass) Classification Fe O Cu and inevitable impuritiesCu alloy powders A 1.2 0.25 balance B 4.1 0.36 balance C 9.5 0.52balance D 5.2 0.35 balance E 3.8 0.68 balance F 8.5 0.94 balance G 2.90.31 balance H 4.6 0.58 balance I 7.7 0.67 balance J 6.3 0.42 balance K3.8 0.98 balance L 4.2 0.13 balance

These raw powders were formulated according to the compositions shown inTable 9 and mixed with zinc stearate powder, as a lubricant used uponmetallic molding, in an amount of 0.8% in terms of an outer percentage,and then the powder mixture was press-formed into a bar-shaped greencompact measuring 10 mm×10 mm×50 mm under a compacting pressure of 600MPa. The resulting bar-shaped green compact was sintered in anendothermic gas atmosphere under the conditions of a temperature of1140° C. for 20 minutes to obtain bar-shaped test pieces of Examples C1to C10 each having the composition shown in Table 9 to Table 11,bar-shaped test pieces of Comparative Examples C1 to C6 and a bar-shapedtest piece (Conventional Example C1) made of a conventional iron-basedsintered alloy.

With regard to Examples C1 to C10, Comparative Examples C1 to C6 andConventional Example C1, concentration distribution of Cu and O in thebasis material texture was observed by EPMA. The results are shown inTable 9 to Table 11. The size of these bar-shaped test pieces wasmeasured and a dimensional change ratio of a standard size of the greencompact was determined. The dimensional accuracy was evaluated by theresults shown in Table 11. A Charpy impact value was determined by aCharpy impact test. The results are shown in Table 11. Furthermore,Examples C1 to C10, Comparative Examples C1 to C6 and ConventionalExample C1 were machined to obtain tensile test pieces. Using thesetensile test pieces, tensile strength was measured. The results areshown in Table 11.

Furthermore, Examples C1 to C10, Comparative Examples C1 to C6 andConventional Example C1 were machined to obtain wear test pieces eachmeasuring 5 mm×10 mm×45 mm and a SCM420 ring having an outer diameter of40 mm and an inner diameter of 27 mm. Using the wear test pieces andring, the following wear test was conducted and sliding properties wereevaluated by the results shown in Table 11.

Wear Test 1

Each wear test piece was pressed against the ring rotating at arotational speed of 3 m/second while increasing a pressing load, andthen a load at which seizing occurred (load upon seizing) was measured.Sliding properties were evaluated by the results shown in Table 11.

Wear Test 2

Each wear test piece was pressed against the ring rotating at arotational speed of 3 m/second under a load of 20 kgf. After mounting astrain gage in a direction horizontal to a pressing direction, the loadcalculated from the value of the strain gage was divided by the abovepressing load (20 kgf), thereby to obtain a friction coefficient.Sliding properties were evaluated by the results shown in Table 11.TABLE 9 Composition of raw powder (% by mass) Cu alloy Iron-based powderin Graphite Fe Composition (% by mass) sintered alloys Table 8 powderpowder Cu C O Fe Texture Examples C1 A: 0.6 0.8 balance 0.6 0.71 0.02balance Aggregate of base C2 B: 2 0.8 balance 1.8 0.72 0.04 balancematerial cells C3 C: 3 0.8 balance 2.8 0.71 0.06 balance wherein the C4D: 5 0.8 balance 4.7 0.73 0.08 balance concentration of C5 E: 7 0.8balance 6.6 0.73 0.13 balance Cu and O in the C6 F: 11 0.8 balance 9.80.72 0.28 balance vicinity of an old C7 G: 3 0.15 balance 2.9 0.12 0.04balance Fe powder boundary C8 H: 3 0.3 balance 3.0 0.28 0.07 balance ishigher than the C9 I: 3 0.6 balance 3.0 0.54 0.09 balance concentrationof Cu C10 J: 3 0.11 balance 2.6 0.97 0.05 balance and O of the centerportion

TABLE 10 Composition of raw powder (% by mass) Cu alloy Iron-basedpowder in graphite Fe Composition (% by mass) sintered alloys Table 8powder powder Cu C O Mn Fe Texture Comparative C1 K: 11 0.8 balance 9.80.71  0.31* — balance Aggregate of base material cells Examples C2 L:0.6 0.8 balance 0.6 0.72  0.01* — balance wherein the concentration ofCu and O C3 B: 3 0.1 balance 2.9  0.06* 0.05 — balance in the vicinityof an old Fe powder C4 B: 3 1.2 balance 2.8  1.10* 0.05 — balanceboundary is higher than the concentration C5 B: 12 0.8 balance 11.5*0.70 0.12 — balance of Cu and O of the center portion C6 B: 0.4 0.8balance  0.4* 0.71 0.03 — balance Conventional Pure Cu: 3 0.8 balance2.9 0.72 0.03 0.027 balance MnO grains are dispersed in a basismaterial. Example C1 MnO: 0.1Note:symbol * denotes a value that is not within the scope of the presentinvention

TABLE 11 Dimensional Charpy Load change impact Tensile upon FrictionIron-based ratio value strength seizing coef- sintered alloys (%)(J/cm²) (MPa) (N) ficient Examples C1 0.01 25 596 686 0.17 C2 0.01 18620 588 0.15 C3 0.05 22 567 686 0.12 C4 0.10 20 663 725 0.11 C5 0.14 19642 993 0.08 C6 0.16 17 695 594 0.04 C7 0.12 24 563 630 0.15 C8 0.08 26572 705 0.12 C9 0.07 24 645 685 0.11 C10 0.03 23 623 673 0.13Comparative C1 0.42 4 431 553 0.29 Examples C2 0.10 10 238 200 0.32 C30.18 9 351 215 0.24 C4 0.13 8 225 235 0.26 C5 0.55 5 405 264 0.21 C60.12 10 380 245 0.31 Conventional 0.36 7 375 180 0.33 Example C1

As is apparent from the results shown in Table 9 to Table 11, comparingbar-shaped test pieces of Examples C1 to C10 with the bar-shaped testpiece of Conventional Example C1, the bar-shaped test pieces of ExamplesC1 to C10 are superior in dimensional accuracy because a dimensionalchange ratio is smaller than that of the test piece made of ConventionalExample C1, and exhibit high Charpy impact value and high tensilestrength. Also the bar-shaped test pieces of Examples C1 to C10 are madeof alloys which are less likely to cause seizing because of largeseizing load, and are superior in sliding properties because ofdrastically small friction coefficient.

However, test pieces of Comparative Examples C1 to C6, which have acomposition that is not within the scope of the third aspect, areinferior in at least one of dimensional accuracy, Charpy impact value,tensile strength and wear amount.

INDUSTRIAL APPLICABILITY

The iron-based sintered alloy, the iron-based sintered alloy member andthe oil pump rotor of the present invention are superior in dimensionalaccuracy, strength and sliding properties and can remarkably contributeto the development of the mechanical industry.

1. A method of manufacturing an iron-based sintered alloy member havinga composition consisting of 0.5 to 7% by mass of Cu, 0.1 to 0.98% bymass of C, 0.02 to 0.3% by mass of oxygen, and the balance of Fe andinevitable impurities, the method comprising: formulating an Fe powder,a graphite powder and a Cu alloy powder, as raw powders; mixing thepowders to form a powder mixture; and forming the powder mixture into agreen compact and sintering the green compact; wherein the Cu alloypowder has a composition consisting of 1 to 10% by mass of Fe, 0.2 to 1%by mass of oxygen, and the balance of Cu and inevitable impurities.
 2. Amethod of manufacturing an iron-based sintered alloy member having acomposition consisting of 0.5 to 7% by mass of Cu, 0.1 to 0.98% by massof C, 0.02 to 0.3% by mass of oxygen, 0.0025 to 1.05% by mass of Mnand/or 0.001 to 0.7% by mass of Zn, and the balance of Fe and inevitableimpurities, the method comprising: formulating an Fe powder, a graphitepowder and a Cu alloy powder, as raw powders; mixing the powders to forma powder mixture; forming the powder mixture into a green compact andsintering the green compact, wherein the Cu alloy powder has acomposition consisting of 1 to 10% by mass of Fe, 0.2 to 1% by mass ofoxygen, 0.5 to 15% mass of Mn and/or 0.2 to 10% by mass of Zn, and thebalance of Cu and inevitable impurities.
 3. (canceled)
 4. (canceled) 5.A method of manufacturing an iron-based sintered alloy member having acomposition consisting of 0.5 to 7% by mass of Cu, 0.1 to 0.98% by massof C, 0.02 to 0.3% by mass of oxygen, 0.001 to 0.14% by mass in total ofat least one selected from the group consisting of Al and Si, and thebalance of Fe and inevitable impurities, the method comprising:formulating an Fe powder, a graphite powder and a Cu alloy powder, asraw powders; mixing the powders to form a powder mixture; and formingthe powder mixture into a green compact and sintering the green compact,wherein the Cu alloy powder has a composition consisting of 1 to 10% bymass of Fe, 0.2 to 1% by mass of oxygen, 0.01 to 2% by mass in total ofat least one selected from the group consisting of Al and Si, and thebalance of Cu and inevitable impurities.
 6. A method of manufacturing aniron-based sintered alloy member having a composition consisting of 0.5to 7% by mass of Cu, 0.1to 0.98% by mass of C, 0.02 to 0.3% by mass ofoxygen, 0.0025 to 1.05% by mass of Mn and/or 0.001 to 0.7% bv mass ofZn, 0.001 to 0.14% by mass in total of at least one selected from thegroup consisting of Al and Si, and the balance of Fe and inevitableimpurities, the method comprising: formulating an Fe powder, a graphitepowder and a Cu alloy powder, as raw powders; mixing the powders to forma powder mixture; and forming the powder mixture into a green compactand sintering the green compact, wherein the Cu alloy powder has acomposition consisting of 1 to 10% by mass of Fe, 0.2 to 1% by mass ofoxygen, [[and]] 0.5 to 15% by mass of Mn and/or 0.2 to 10% by mass ofZn, 0.01 to 2% by mass in total of at least one selected from the groupconsisting of Al and Si, and the balance of Cu and inevitableimpurities.
 7. (canceled)
 8. (canceled)
 9. The method of manufacturingthe iron-based sintered alloy member according to claim 1, wherein theFe powder, the graphite powder and the Cu alloy powder are formulated sothat the content of the graphite powder is from 0.1 to 1.2% by mass, thecontent of the Cu alloy powder is from 1 to 7% by mass, and the balanceis composed of the Fe powder.
 10. An oil pump rotor made of aniron-based sintered alloy, comprising an iron-based sintered alloyhaving a composition consisting of 0.5 to 7% by mass of Cu, 0.1 to 0.98%by mass of C, 0.02 to 0.3% by mass of oxygen, and the balance of Fe andinevitable impurities.
 11. An oil pump rotor made of an iron-basedsintered alloy, comprising an iron-based sintered alloy having acomposition consisting of 0.5 to 7% by mass of Cu, 0.1 to 0.98% by massof C, 0.02 to 0.3% by mass of oxygen, 0.0025 to 1.05% by mass of Mnand/or 0.001 to 0.7% by mass of Zn, and the balance of Fe and inevitableimpurities.
 12. (canceled)
 13. (canceled)
 14. An oil pump rotor made ofan iron-based sintered alloy, comprising an iron-based sintered alloyhaving a composition consisting of 0.5 to 7% by mass of Cu, 0.1 to 0.98%by mass of C, 0.02 to 0.3% by mass of oxygen, 0.001 to 0.14% by mass intotal of at least one selected from the group consisting of Al and Si,and the balance of Fe and inevitable impurities.
 15. An oil pump rotormade of an iron-based sintered alloy, comprising an iron-based sinteredalloy having a composition consisting of 0.5 to 7% by mass of Cu, 0.1 to0.98% by mass of C, 0.02 to 0.3% by mass of oxygen, 0.0025 to 1.05% bymass of Mn and/or 0.001 to 0.7% by mass of Zn, 0.001 to 0.14% by mass intotal of at least one selected from the group consisting of Al and Si,and the balance of Fe and inevitable impurities.
 16. (canceled) 17.(canceled)
 18. The oil pump rotor according to claim 10, wherein theiron-based sintered alloy has such a texture that base material cellscontaining Fe, as a main component, Cu and O, which are partitioned withan old Fe powder boundary formed by sintering the Fe powder, as rawpowders, are aggregated to form a basis material and the base materialcells partitioned with the old Fe powder boundary have such a gradientconcentration that the concentration of Cu and O in the vicinity of theold Fe powder boundary is higher than the concentration of Cu and O ofthe center portion of the base material cell.
 19. An iron-based sinteredalloy which has a composition consisting of 0.5 to 10% by mass of Cu,0.1 to 0.98% by mass of C, 0.02 to 0.3% by mass of oxygen, and thebalance of Fe and inevitable impurities, and also has a texture composedof an aggregate of base material cells made of an Fe-based alloycontaining C, Cu and O, which are partitioned with an old Fe powderboundary formed by sintering an Fe powder, as raw powders, wherein thebase material cells made of the Fe-based alloy containing C, Cu and O,which are partitioned with the old Fe powder boundary, have such agradient concentration that the concentration of Cu and O in thevicinity of the old Fe powder boundary is higher than the concentrationof Cu and O of the center portion of the base material cell.
 20. Theiron-based sintered alloy according to claim 19, wherein the basematerial cells made of the Fe-based alloy containing C, Cu and O, whichare partitioned with the old Fe powder boundary, have such a gradientconcentration that the concentration of Cu and O is maximum in thevicinity of the old Fe powder boundary, while the concentration of Cuand O decreases toward the center portion of the base material cell andreached a minimum value at the center of the base material cell.
 21. Amethod of manufacturing the iron-based sintered alloy member of claim19, which comprises formulating an Fe powder, a graphite powder and a Cualloy powder having a composition consisting of 1 to 10% by mass of Fe,0.2 to 1% by mass of oxygen, and the balance of Cu and inevitableimpurities, mixing the powders to form a powder mixture, press-formingthe powder mixture into a green compact and sintering the green compactin a hydrogen atmosphere containing nitrogen at a temperature of 1090 to1300° C.
 22. The method of manufacturing the iron-based sintered alloymember according to claim 2, wherein the Fe powder, the graphite powderand the Cu alloy powder are formulated so that the content of thegraphite powder is from 0.1 to 1.2% by mass, the content of the Cu alloypowder is from 1 to 7% by mass, and the balance is composed of the Fepowder.
 23. The method of manufacturing the iron-based sintered alloymember according to claim 5, wherein the Fe powder, the graphite powderand the Cu alloy powder are formulated so that the content of thegraphite powder is from 0.1 to 1.2% by mass, the content of the Cu alloypowder is from 1 to 7% by mass, and the balance is composed of the Fepowder.
 24. The method of manufacturing the iron-based sintered alloymember according to claim 6, wherein the Fe powder, the graphite powderand the Cu alloy powder are formulated so that the content of thegraphite powder is from 0.1 to 1.2% by mass, the content of the Cu alloypowder is from 1 to 7% by mass, and the balance is composed of the Fepowder.
 25. The oil pump rotor according to claim 11, wherein theiron-based sintered alloy has such a texture that base material cellscontaining Fe, as a main component, Cu and O, which are partitioned withan old Fe powder boundary formed by sintering the Fe powder, as rawpowders, are aggregated to form a basis material and the base materialcells partitioned with the old Fe powder boundary have such a gradientconcentration that the concentration of Cu and O in the vicinity of theold Fe powder boundary is higher than the concentration of Cu and O ofthe center portion of the base material cell.
 26. The oil pump rotoraccording to claim 14, wherein the iron-based sintered alloy has such atexture that base material cells containing Fe, as a main component, Cuand O, which are partitioned with an old Fe powder boundary formed bysintering the Fe powder, as raw powders, are aggregated to form a basismaterial and the base material cells partitioned with the old Fe powderboundary have such a gradient concentration that the concentration of Cuand O in the vicinity of the old Fe powder boundary is higher than theconcentration of Cu and O of the center portion of the base materialcell.
 27. The oil pump rotor according to claim 15, wherein theiron-based sintered alloy has such a texture that base material cellscontaining Fe, as a main component, Cu and O, which are partitioned withan old Fe powder boundary formed by sintering the Fe powder, as rawpowders, are aggregated to form a basis material and the base materialcells partitioned with the old Fe powder boundary have such a gradientconcentration that the concentration of Cu and O in the vicinity of theold Fe powder boundary is higher than the concentration of Cu and O ofthe center portion of the base material cell.